# NODAL_RESIDUAL_OUTPUT

Specifies parameters for outputting the nodal residual.

AcuSolve Command

## Syntax

NODAL_RESIDUAL_OUTPUT {parameters}

## Qualifier

This command has no qualifier.

## Parameters

output_frequency or out_freq (integer) >=0[=0]
Time step frequency at which to output the nodal residual. If zero, this option is ignored.
output_time_interval or out_intv (real) >=0 [=0]
Time frequency at which to output the nodal residual. If zero, this option is ignored.
num_saved_states or save (integer) >=0 [=0]
Number of nodal residual files to keep. If zero, all nodal residual files are kept.

## Description

This command specifies the parameters for writing the nodal residual to disk. For example,
NODAL_RESIDUAL_OUTPUT {
output_frequency      = 100
output_time_interval  = 0
num_saved_states      = 2
}

writes a nodal residual file to disk every 100 time steps as well as the last time step. Only the last two files are kept. Once the third nodal residual file is written to disk, the first nodal residual file is removed to preserve disk space.

NODAL_RESIDUAL_OUTPUT is rarely needed or used. It is used mainly for debugging purposes. At steady state, or at the end of each time step for transient problems, the residual for each equation at each node should be zero. In practice, convergence is assumed if the normalized residuals are within the specified tolerances; see the TIME_SEQUENCE command. If there are difficulties in achieving convergence, the output of this command may be useful in determining where the problem lies.

If either output_frequency or output_time_intervaloutput_time_interval is non-zero, a nodal residual file will be written at the end of the run. If both are zero, no nodal residual files are created.

Run times may not coincide with output_time_interval. In this case, at every time step which passes through a multiple of output_time_interval, nodal residual files are written.

The num_saved_states parameter indicates the number of nodal residual files to save. Once the (num_saved_states + 1)th nodal residual file is written, the first one is removed. When running in parallel, once all files are written (in parallel), then the old ones are removed (in parallel).